A chopping and doubly-fed adjustable speed system without bi-directional converter

A doubly-fed machine adjustable speed system normally needs a bi-directional converter. Not only the control technique is complicated but also the system cost is rather high. In this paper, a chopping and doubly-fed adjusting speed control strategy is proposed based on the variable speed principle of the doubly-fed machine. The circuit topology, fulfilling combined functions of a rectifier, chopper and inverter, is described. The control algorithms in chopping and doubly-fed modes for adjustable speed operation based on the Intel 8XC196MC single-chip-computer are derived. The Experimental results show the feasibility of the proposed scheme. Advantages of using the proposed system include a relatively inexpensive multi-functional converter, soft-starting, adjustable speed operation through chopping and doubly-fed adjustable speed modes below or above synchronous speed with reactive power regulation.